A circulation controlled rotor such as the X-wing, achieves cyclic and collective pitch control by the programmed blowing of pressurized air through leading and trailing edge slots on the blades. The slots are preloaded in a closed position so that when no pressure is supplied to the blade duct, external aerodynamic suction will not cause the slot to open, which would create undesirable drag. The preload also insurres positive, full slot opening at a minimum control pressure which is greater than the preload.
A plenum supplies the pressurized air to the blades via a series of valves. In the case of valve leakage, some pressure may be supplied when none is commanded. This leakage may of itself, or in combination with the aerodynamic suction, cause the slot to open inadvertently.